| Respiratory system |
 |
| A complete, schematic view of the human respiratory system with their parts and functions. |
| Latin |
systema respiratorium |
The respiratory system (or ventilatory system) is the biological system that introduces respiratory gases to the interior and performs gas exchange. In humans and other mammals, the anatomical features of the respiratory system include airways, lungs, and the respiratory muscles. Molecules of oxygen and carbon dioxide are passively exchanged, by diffusion, between the gaseous external environment and the blood. This exchange process occurs in the alveolar region of the lungs.[1] Other animals, such as insects, have respiratory systems with very simple anatomical features, and in amphibians even the skin plays a vital role in gas exchange. Plants also have respiratory systems but the directionality of gas exchange can be opposite to that in animals. The respiratory system in plants also includes anatomical features such as holes on the undersides of leaves known as stomata.[2]
Comparative anatomy and physiology
Horses
Horses are obligate nasal breathers which means that they are different from many other mammals because they do not have the option of breathing through their mouths and must take in oxygen through their noses.
Elephants
The elephant is the only animal known to have no pleural space. Rather, the parietal and visceral pleura are both composed of dense connective tissue and joined to each other via loose connective tissue.[3] This lack of a pleural space, along with an unusually thick diaphragm, are thought to be evolutionary adaptations allowing the elephant to remain underwater for long periods of time while breathing through its trunk which emerges as a snorkel.[4]
Birds
The main section for this topic is on the page
Bird anatomy, in the section
Respiratory system.
The respiratory system of birds differs significantly from that found in mammals, containing unique anatomical features such as air sacs. The lungs of birds also do not have the capacity to inflate as birds lack a diaphragm and a pleural cavity. Gas exchange in birds occurs between air capillaries and blood capillaries, rather than in alveoli.
Reptiles
The anatomical structure of the lungs is less complex in reptiles than in mammals, with reptiles lacking the very extensive airway tree structure found in mammalian lungs. Gas exchange in reptiles still occurs in alveoli however, reptiles do not possess a diaphragm. Thus, breathing occurs via a change in the volume of the body cavity which is controlled by contraction of intercostal muscles in all reptiles except turtles. In turtles, contraction of specific pairs of flank muscles governs inspiration or expiration.[5]
Amphibians
Both the lungs and the skin serve as respiratory organs in amphibians. The skin of these animals is highly vascularized and moist, with moisture maintained via secretion of mucus from specialized cells. While the lungs are of primary importance to breathing control, the skin's unique properties aid rapid gas exchange when amphibians are submerged in oxygen-rich water.[6]
Fish
In most fish, respiration takes place through gills. (See also aquatic respiration.) Lungfish, however, do possess one or two lungs. The labyrinth fish have developed a special organ that allows them to take advantage of the oxygen of the air.
Anatomy in invertebrates
Insects
Most insects breath passively through their 'Spiracles' (special openings in the exoskeleton) and the air reaches the body by means of a series of smaller and smaller pipes called 'trachaea' when their diameter is relatively large and 'tracheoles' when their diameter is very small. Diffusion of gases is effective over small distances but not over larger ones, this is one of the reasons insects are all relatively small. Insects which do not have spiracles and trachaea, such as some Collembola, breathe directly through their skins, also by diffusion of gases.[7] The number of spiracles an insect has is variable between species, however they always come in pairs, one on each side of the body, and usually one per segment. Some of the Diplura have eleven, with four pairs on the thorax, but in most of the ancient forms of insects, such as Dragonflies and Grasshoppers there are two thoracic and eight abdominal spiracles. However in most of the remaining insects there are less. It is at this level of the tracheoles that oxygen is delivered to the cells for respiration. The trachea are water-filled due to the permeable membrane of the surrounding tissues. During exercise, the water level retracts due to the increase in concentration of lactic acid in the muscle cells. This lowers the water potential and the water is drawn back into the cells via osmosis and air is brought closer to the muscle cells. The diffusion pathway is then reduced and gases can be transferred more easily.
Insects were once believed to exchange gases with the environment continuously by the simple diffusion of gases into the tracheal system. More recently, however, large variation in insect ventilatory patterns have been documented and insect respiration appears to be highly variable. Some small insects do demonstrate continuous respiration and may lack muscular control of the spiracles. Others, however, utilize muscular contraction of the abdomen along with coordinated spiracle contraction and relaxation to generate cyclical gas exchange patterns and to reduce water loss into the atmosphere. The most extreme form of these patterns is termed discontinuous gas exchange cycles (DGC).[8]
Molluscs
Molluscs generally possess gills that allow exchange of oxygen from an aqueous environment into the circulatory system. These animals also possess a heart that pumps blood which contains hemocyaninine as its oxygen-capturing molecule. Hence, this respiratory system is similar to that of vertebrate fish. The respiratory system of gastropods can include either gills or a lung.
Physiology in mammals
Ventilation
In respiratory physiology, ventilation (or ventilation rate) is the rate at which gas enters or leaves the lung. It is categorized under the following definitions:
[citation needed] Most plants have relatively few living cells outside of their surface because air (which is required for metabolic content) can penetrate only skin deep. However, most plants are not involved in highly aerobic activities, and thus have no need of these living cells.
References
- ^ Maton, Anthea; Jean, Hopkins Susan, Johnson Charles William, McLaughlin Maryanna Quon Warner David, LaHart Wright, Jill (2010). Human Biology and Health. Englewood Cliffs: Prentice Hall. pp. 108–118. ISBN 0134234359.
- ^ West, John B. Respiratory physiology-- the essentials. Baltimore: Williams & Wilkins. pp. 1–10. ISBN 0-683-08937-4.
- ^ West, John B.; Ravichandran (1993). "Snorkel breathing in the elephant explains the unique anatomy of its pleura". Respiration Physiology 126 (1): 1–8. doi:10.1016/S0034-5687(01)00203-1. PMID 11311306.
- ^ West, John B. (2002). "Why doesn't the elephant have a pleural space?". News Physiol Sci 17: 47–50. PMID 11909991.
- ^ Respiratory system. Encyclopædia Britannica.
- ^ Gottlieb, G; Jackson DC (1976). "Importance of pulmonary ventilation in respiratory control in the bullfrog". Am J Physiol 230 (3): 608–13. PMID 4976.
- ^ The Earth Life Web, Insect Morphology and Anatomy. Earthlife.net. Retrieved on 2013-04-21.
- ^ Lighton, JRB (January 1996). "Discontinuous gas exchange in insects". Annu Rev Entomology 41: 309–324. doi:10.1146/annurev.en.41.010196.001521.
- ^ The combination of a crying baby and a frustrated parent or caregiver CAN BE DEADLY. Saskatchewan Prevention Institute. usask.ca.
- ^ "Respiration". Harvey Project. Retrieved 27 July 2012.
- ^ A simple model of how the lungs are inflated can be built from a bell jar
- ^ Roberts, Fred (2000). "Respiratory Physiology". Update in Anaesthesia (12).
- ^ Michelle, Julia (March 7, 2011). "How Do Babies Breathe in the Womb?".
- ^ Sullivan, LC; Orgeig, S (2001). "Dexamethasone and epinephrine stimulate surfactant secretion in type II cells of embryonic chickens". American journal of physiology. Regulatory, integrative and comparative physiology 281 (3): R770–7. PMID 11506991.
- ^ Premature Babies, Lung Development & Respiratory Distress Syndrome. Pregnancy-facts.com.
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